In the field of self-clinching fasteners, there is a need to design fasteners that have improved torque-out (rotational) and push-out resistance. Self-clinching fasteners are generally well-known in the art and have many different designs. Self-clinching fasteners attach to metal sheets, substrates, or openings in ductile material without welding or additional fasteners. When typical self-clinching fasteners are pressed into pre-punched, drilled, or reamed holes in ductile metal, the ductile metal cold flows into recesses and features of the self-clinching fastener to secure it to the metal. The recesses and features of existing self-clinching fasteners take a variety of forms, including knurls, ribs, and serrated clinching rings to name a few. Typical self-clinching fasteners utilize tooling in the die to locally compress the ductile metal into a recess on the fastener to secure it to the ductile metal. Once a self-clinching fastener is inserted into the ductile metal, the self-clinching fastener is permanently attached to the metal, and removal of the fastener results in either failure of the metal or the fastener.
Existing self-clinching fasteners suffer from a number of shortcomings such as limited torque-out resistance and limitations regarding the thickness of metal and shape of the hole into which the self-clinching fastener may be secured. Typical self-clinching fasteners require very tight tolerances in both the fastener itself and the hole into which the fastener is being installed. In particular, tight tolerances exist for both the size of the hole and the thickness of the sheet. The reason for tight hole size and sheet thickness tolerances is two-fold. First, existing self-clinching fasteners include features that prevent rotation of the fastener. Such features provide recesses or pockets into which the ductile metal cold flows during installation. Examples of the features are serrated rings, knurled studs, ribs, or a hexagonal shaped head that embeds into the surface of the metal. Second, there must be enough material immediately around the hole to cold flow into the various recesses and features of the self-clinching fastener to secure the fastener to the sheet and provide adequate push-out resistance. For example, if a self-clinching fastener is pressed into a hole that is slightly too large for the fastener, there may be insufficient material to flow into the recesses and features of the fastener thereby causing the connection between the fastener and the metal sheet to be weaker than anticipated and the fastener may fail during normal use.
Additionally, as sheet thickness increases, existing self-clinching fasteners sometimes require additional machining such as drilling and/or counter-boring of the ductile metal combined with special die tooling to adequately compress the ductile metal into the recesses of the self-clinching fastener to securely clinch the fastener. Such additional machining and special die tooling are often prohibitively expensive. Self-clinching fasteners for thick materials typically use knurled shoulder sections to resist torque-out. However knurls have shallow tooth depth, making them ill-suited for rough punched holes. The inner diameters of rough punched holes are tapered due to the punch process causing loss of engagement with the knurls. Subsequent hole reaming is often needed to prevent torque-out of such knurled-shoulder self-clinching fasteners.
Thus, there is a need for a self-clinching fastener that has high resistance to torque-out and push-out, can be attached to material of varying thickness, and can be attached to holes that do not have special geometry or pre-formed, or post-machined surfaces.